Obstructive sleep apnea occurs commonly in obese overweight older men. It is associated with fragmented and hypoxemic sleep that leads to a major early clinical feature of daytime hypersomnolence. Other associated features include systemic and pulmonary hypertension, cardiac arrhythmias, and sudden death. While sleep apnea represents an extreme form of obstructed breathing, it appears that many older individuals who snore and demonstrate partial airflow obstruction are at increased risk of developing clinically significant illness. The major purpose of this proposal is to identify patients at high risk for at developing obstructive sleep and determine the increased morbidity over time. We will identify high risk patients by determining the degree of collapsibility of the upper airway and evaluate the effects of weight loss and exercise in the prevention of this disorder (Specific Aim #2). The major determinant of increased clinical illness will be assessed by characterizing sleep architecture; the development of daytime hypersomnolence and alterations in neurocognitive function (Specific Aim #1). This project involves complete physiologic monitoring in a sleep laboratory including electroencephalographic, electrocardiographic, and respiratory and oxygenation recordings. Measurements of upper airway collapsibility will be made utilizing special catheters placed in the upper airway.